Use of Legumes in Pecan Orchards - OSU Fact Sheets - Oklahoma ...

Oklahoma Cooperative Extension Service
HLA-6250
Use of Legumes
in Pecan Orchards
Dean McCraw
Extension Horticulturist
Tree Fruit and Pecan
Michael Smith
Professor, Department of
Horticulture & Landscape Architecture
Oklahoma’s approximately 80,000 acres of managed
pecans contribute about $15 million each year to the state’s
agriculture economy. Acreage estimates of unmanaged native
pecans in Oklahoma vary but are conceded to be in excess of
100,000 acres. Most of Oklahoma’s pecans are from improved
native groves, most of which also support livestock during part
of the season.
A mature pecan orchard consists of two separate but
interrelated ecosystems. The orchard floor provides a working
surface for orchard operations and influences activities in
the tree canopy which produces the pecan crop. Oklahoma’s
planted pecan orchards usually consist of native vegetation on
the orchard floor with a clean strip 6' to 12' wide along the tree
row. Vegetation weed-free strips are normally maintained with
herbicides while the vegetation in row middles is maintained by
mowing. The mowed sod middle prevents or reduces erosion,
improves wet weather trafficability for spraying and other orchard
operations and can provide forage for grazing livestock. Due to
irregular tree spacing improved native groves often utilize sod
culture throughout.
A good orchard floor cover does not compete excessively
with trees for moisture or nutrients and is compatible with orchard
insect populations. The importance of vegetation management
in the orchard floor is documented. Weed competition with tree
roots is significant throughout the tree life. Weed competition
in newly planted pecan orchards decreases survival and severely
retards tree growth. Weed competition even with mature
trees can reduce tree growth and yield as well as contribute
to alternate bearing. Pecan trees have an extensive root system
including a tap root which penetrates as deep as the soil
structure and water table will permit. The bulk of the pecan’s
nutritional needs, however, are met by small feeder roots which
are located near the soil surface. It is these roots which come
into direct competition with vegetation on the orchard floor. An
effective orchard floor management program integrates the
needs of the cover with the needs of the trees with respect to
rooting depth, extent of rooting and time of year when water
and nutrient demand peak.
Sod-free culture in pecan orchards is discouraged due to
increased erosion, decreased wet weather accessibility in the
orchard and a poor harvest surface. A vegetation-free orchard
floor also loses moisture faster than a properly managed sod
and is dusty during harvest. Tillage equipment is prone to inflict
injury to trunks and frequently damages shallow feeder roots
which provide nutrients and water to trees. A well managed
orchard floor cover facilitates harvest and provides grazing for
livestock.
Oklahoma Cooperative Extension Fact Sheets
are also available on our website at:
http://osufacts.okstate.edu
Nitrogen Needs of Pecans
Mature pecan trees require 100 to 150 lbs. of nitrogen (N)
per acre annually to grow and produce properly. Adequate N
must be available at budbreak to support vegetative growth and
leaf expansion which occurs immediately and relatively rapidly
after budbreak. The nutritional needs of the orchard cover crop
as well as the trees must be in concert. Ideally, peak demands
of each would occur at different times of the year.
Insects
Hundreds of species of arthropods, i.e. insects, mites and
spiders, are present in pecan orchards. Fortunately, most are
noninjurious to the pecan and many are beneficial; feeding
on those which inflict damage to pecan tree leaves, twigs or
nuts.
Harmful insects include various kinds of aphids, worms
and true bugs as well as phylloxera, mites, spittlebugs and
weevils.
Nature provides some natural pest control by the presence
of insects which feed on other arthropods. Some of
the most common predators include various species of lady
beetles, lacewings, assassin bugs, spiders, and others. See
OSU Extension Fact Sheet 7307 for additional information on
beneficial insects.
An effective orchard pest management program manages
the orchard ecosystem to attract beneficial insects to
the orchard and retain them in numbers sufficient to combat
infestations of harmful insects. This usually involves provision
of a food source, e.g. aphids. The beneficials must then follow
the food source, e.g. aphids, up into the trees as the ground
cover growth slows or goes dormant.
Benefits of Legumes
Legumes as the ground cover in pecan orchards offer
two advantages over typical grass ground covers. First, N is
fixed, i.e., removed from the air by bacteria associated with the
legume roots and utilized by the legume. When the legume root
and top decompose, stored N in the legume is released and
available to the pecan tree. Second, certain legumes harbor
large aphid densities which attract beneficial insects that feed
on aphids and other insects. When the aphid densities on the
legume decline or the legumes senesce, the beneficial insects
associated with the legumes seek another food source such
as aphids and other pests in the pecan canopy. Therefore,
proper selection and management of legumes as the orchard
floor cover may reduce or eliminate the need for supplemental
Division of Agricultural Sciences and Natural Resources • Oklahoma State University

N fertilization and may reduce the number of pesticide applications
necessary for pecan production.
Characteristics of Legumes
Certain characteristics of legumes are more compatible
with pecan production. First, a cool season legume is less
competitive with the trees for soil moisture than a warm season
legume, plus the cool season legume would stimulate an
earlier increase in the beneficial insects. The legume should
be tolerant to both sun and shade. Many pecan orchards are
prone to flooding; therefore, flooding tolerance is desirable.
Also, the legume must not cause an increase in undesirable
insects, such as stink bugs, while attracting beneficial insects.
The legume should also be capable of fixing large quantities of
N. Additionally, the legume must be capable of withstanding the
traffic associated with orchard maintenance and harvesting.
Legume Selection and Establishment
Arrowleaf is a heavy forage producer, while ‘Dixie’ crimson
and ‘Kenland’ red clovers produce more N. Larger scale tests
indicate total N production from some legumes exceeds 100
lbs/A. Aphid densities tend to be higher on crimson, arrowleaf,
subterranean, and red clovers. Beneficial Lady beetle adult
and larval densities are higher on crimson, red, and arrowleaf
clovers. Other prominent beneficials found in clovers include
green lacewings, soldier beetles, predacious stink bugs, damsel
bugs and hover flies. As the legumes decline with the onset
of hot weather in June the beneficials move up into the trees
and feed on aphids.
White clover are more flood tolerant than red and annual
clovers.
Perennial legumes, e.g. red and white clover, also appear
to be better adapted over a wide range of soils including
relatively heavy silt loan soils than are annuals. Perennial
legumes may attract stink bugs, which can damage pecans by
feeding on the nuts. To avoid damage, legumes should not be
mowed between August 1 and shuck split. This should retain
stink bugs in the ground cover rather than forcing them into
the trees. Also, trees should be scouted carefully to determine
if stink bug control becomes necessary.
Effective legume mixtures for pecan orchards are shown
in Table 1. Due to seed size differences between legume
species, separate seeding operations for each legume are
required to achieve the recommended seeding rates. Legume
seed should be inoculated with the appropriate Rhizobium
spp. prior to planting. Soil, seed contact, and moisture are essential
for successful establishment. Existing stubble should
be mowed or grazed closely prior to seeding. Seeding with a
pasture drill is generally the most dependable. However, light
disking prior to broadcast seeding followed by rolling can also
result in acceptable stand establishment. Growers should soil
test and ensure adequate phosphorous and potassium prior
to seeding. Additional information on legume establishment is
contained in OSU Fact Sheet PSS-2585, “Forage Legumes
for Oklahoma.”
Either annuals or perennials can be used. Vetch usually
lasts longer than the clover. Reseeding of crimson clover may
be needed each fall. In the perennial mix, the white clover
produces more N while the red clover attracts more beneficial
insects. Close mowing or grazing in late summer improves
stand return in most cases.
Grazing livestock on orchard legumes reduces N availability
to the pecans, but legumes provide a high quality forage
and rapid weight gain for cattle. Growers who choose to graze
should exercise due caution with respect to bloat prevention.
Consult your county extension educator in this regard.
Whether or not orchards are grazed, a leaf sampling
program should be followed to ensure that the legumes are
meeting the N needs of the trees. Broadcast N applications on
actively growing legumes tend to reduce the legume stands
and decrease the amount of N fixed by the legume. If the trees
require supplemental N applications, it should be broadcast in
early June when legumes begin to senesce or become inactive
during the summer. Information on pecan leaf sampling is in OSU
Fact Sheet 6232, “Fertilizing Pecan and Fruit Trees.” Legumes
must also be utilized in conjunction with a good insect scouting
program to determine the need for pesticide applications.
Table 1. Recommended annual and perennial legumes for use as pecan orchard cover crops.
Approximate
Seeding seed cost Seeding
Legume Habit rate (lb/A) ($/lb) time
‘Dixie’ Crimson Clover Annual 10 1.00 early Oct.
+
Hairy Vetch Annual 8 .60 early Oct.
‘Kenland’ Red Clover Perennial 8 1.20 early Oct.
+
‘Louisiana S-1’ White Clover Perennial 2 2.50 early Oct.
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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Robert E. Whitson, Director of Cooperative Extension
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